Traditionally, sub-surface safety valves (SSSV) have had a flat or curved closure element known as a flapper, or a ball-shaped closure element, which rotates approximately 90 degrees, from opened to closed positions, under the bias of a closure spring generally mounted to the hinge holding the closure element to the valve body. The closure spring acts on the closure element after a flow tube or other actuating element is retracted. The flow tube and actuator mechanism are typically mounted above the closure element and inside the seat against which the closure element contacts for closure. The flow tube and actuator are biased in the uphole (closed) direction by a separate spring, commonly known as the power spring, and are driven down against the spring bias and into the closure element by pressure (or other appropriate signal) delivered through a control line extending to the SSSV from the surface. As long as control line pressure (or other appropriate signal) is applied to the actuator the power spring bias on the flow tube is overcome and the flow tube stays in a down (open) position. In the down position of the flow tube, the closure element is rotated against the bias of the closure spring, and away from contact with the mating seat. The closure element winds up behind or adjacent to the flow tube when the SSSV is open. If control line pressure (or signal) is lost, the power spring bias on the flow tube pushes it and the actuator mechanism uphole. This movement, in turn, allows the closure spring, acting on the closure element, to rotate the closure element on its hinge in an uphole direction until it makes contact with the mating seat.
Traditionally, the flow tube and the actuator mechanism have always been above the closure element. This required the bias (power) spring on the flow tube to support the weight and overcome friction of the flow tube as well as to bias it uphole to allow the closure element to shut. Since the flapper had to rotate 90 degrees in the uphole direction to close the SSSV, a hinge closure spring was always necessary to create that motion to overcome the weight of the flapper and apply a contact force to it to hold it against its mating seat. As a result of this configuration, the overall length of SSSVs was longer than it needed to be. In low pressure applications, there was concern about the ability of the closure spring on the flapper to apply a sufficient closing force against the mating seat to keep the SSSV closed. This concern also arose when there was sand, paraffin, asphaltine or other friction increasing compounds in the well fluids, creating doubt as to the available closure force on the flow tube from its power spring. If the flow tube gets stuck, the SSSV cannot close.
The present invention presents a unique design where the actuator mechanism is below the flapper. The power spring acts on a sleeve or rod operably connected to the flapper on an opposed side of the pivot mounting. The spring pushes the sleeve or rod downhole to rotate the flapper closed, upon loss of control line signal. The details and other features of the invention will become more readily apparent from a detailed review of the description of the preferred embodiment, which appears below.